Reflecting electric lamp



Nov. 12, 1940. c. BIRDSEYE REFLECTING ELECTRIC LAMP Filed Oct. 3, 1938Patented Nov. 12, 1940 4 PATENT OFFICE REFLECTING ELECTRIC LAMP ClarenceBirdseye, Gloucester, Mass, assignor, by mesne assignments, to BirdseyeElectric Corporation, Gloucester, Masa, a corporation of MassachusettsApplication October 3, 1938, Serial No. 232,917

5 Claims. (01. 176-34) This invention relates to reflecting electriclamps, that is to say, to lamps having bulbs provided with a reflectingcoating for controlling the intensity or direction of their lightoutput.

5 In one aspect my invention consists in an improved lamp having areflecting coating upon its inner surface in an area enclosing its lightsource and an external opaque coating upon a substantially coextensivearea. In another aspect the invention consists in a novel process ofmanufacturing reflecting lamps of this character.

It has long been appreciated that a thin metallic coating deposited uponthe surface of a lamp bulb is a more eflicient reflector than a coatingotherwise similar but of greater thickness. This is probably due to thefact that the thicker coating presents a more irregular surface tendingto cause greater diiiusion of the'light than a thin metallic coatingwhich may approach a mono-molecular thickness and so present anextremely smooth surface. It is difhcult under commercial conditions ofmanufacture to apply a thin metallic coating which is continuous andfree from pinholes and other imperfections that detract seriously fromthe appearance of the lamp, particularly when illuminated. I havediscovered, however, that a thin and possibly imperfect inner metallic.coating may be supplemented by a thicker outer opaque coating in suchmanner that all the advantages of a very thin and highly efiicientinternal coating may be retained and still the combined inner and outercoating of the lamp as a whole be free of visible holes, thin spots orother defects.

,In accordance with the present invention the inner metallic coating maybe applied to the i or inner surface of the bulb in any convenient man--ner, as by depositing from a metallic solution or by vaporizing underconditions of reduced -pres sure. The internal coating may then berestricted to the desired area within the bulb, by removing theundesired portion of the coating chemically or mechanically.Subsequentlyan external metallic or other opaque coating may be appliedto the outer surface of the bulb in any desired manner, as by spraying,and may be confined to an area substantially coincident with the innermetallic coating of the bulb. The external coating may be applied at anyconvenient stage in the manufacturing process, either before or afterthe mount and filament have been scaled into the bulb. One verysatisfactory way of applying the external coatingis to protectappropriate portions of the bulb by an enveloping shield and spray ametallic laquer upon the exposed portions of the bulb up to the line ofthe shield. Anadvantage of carrying out this step in the mannersuggested is that theexternal coating may thus be applied to otherwisecompleted lamps. The process is, therefore, available 5 forafter-treating lamps which testshave shown to have defective internalcoatings or for correcting or increasing the area of the compositereflecting coating of lamps already otherwise completed. w

These and other features of the invention will be best understood andappreciated from the following description of a preferred manner ofcarrying outthe novel process thereof in producing a reflecting lamp oia type selected for 15 purposes of illustration. In the drawing- 7 IFig. 1 is a view inelevation with parts broken away of a lamp bulb,

Fig. 2 is a. view in elevation of the bulb inverted and in process ofhaving an internal coat- 20 ing applied to it,

Fig. 3 is a view in elevation of the bulb internally coa-Ied, suggestingthe step of removing the internal coating up to the line of maximum 7bulb diameter, 25

Fig. 4 is a view in elevation of-the bulb suggesting the step ofapplying the external coating, and

Fig. 5 is a fragmentary View in cross section of part of the completedlamp. 30

This invention is herein illustrated in the treatment of a pear-shapedbulb of conventional designbut it is, of course, not limited in itsapplication to this or to any particular type of bulb or lamp. 'I'he-bulb Ill, after being first 36 properly cleaned, is inverted andmounted in apparatus in which is included a sealing disk I I, an exhauststem i2 and leads. l3 carrying a re-' .ceptacle H for a pellet of silveror aluminum. The bulb thus mounted is exhausted and heated 40 and then aheavy current is caused to flow in the leads i3 heating the receptaclel4 and causing the metal therein to be vaporized and to be deposited asa thin metallic film or coating upon the inner surface of the bulb. ".hecoating thus 45 deposited may be distributed generally over the entireinner surface of the bulb, although by properly locating the recept'acleHi the coating may be more or less localized. For example, as shown inFig. 1, a smaller amount of metal will be deposited in the neck portionsof the bulb than in its bowl end. The internal coating 15 may be madevery thin by limiting the amount of metal supplied in the receptacle andcontrolling the conditions under which it is flashed or vaporized.However the internal coating I5 may be applied it will be understoodthat it is deposited upon the surface of the bulb as a very thin film ofhigh lustre and, while it is desirable that the film should becontinuous, the occurrence of pinholes or thin spots, if any, is takencare of and covered up by the external coating subsequently applied.

The bulb I 0 may initially have a clear, untreated inner surface or itmay be frosted as suggested in Figs. 1 and 2. If the bulb is frcste" itshould be done very lightly and under these circumstances the internalreflecting coating will have a slight diffusing effect instead of beingentirely specular in its action as is the case when an unfrosted bulb isused.

In Fig. 2 a frosted bulb in is shown in position for evacuation anddeposition of an internal coating by the process of evaporation. Theinternal coating [5 which is applied in this manner is indicated in thebulb as shown in Fig. 3 and this figure also indicates the step ofremoving the coating 15 up to the line of maximum bulb diameter.

The inverted bulb is sealed by a stopper I6 through which passes anouter vertical conduit l1 and an inner tube 18 having a filter [9 at itsupper end. A solvent solution is introduced into the bulb through thetube It up to the desired level which in this case is the line ofmaximum bulb diameter. The solvent solution is introduced slowly and isprevented from splashing by the filter l9 so that the coating above theliquid level 'of the solution is guarded from damage during the removingstep. In any case the solvent solution is supplied to a liquid leveldetermined by the overflow outlet supplied by the outer tube N. Fig. 4indicates that the internal coating I 5 has been removed up to thespecified line and is now limited to the bowl portion of the bulb abovethe line of maximum bulb diameter.

The next step of the process consists in applying an external reflectingcoating to the bowl portion of the bulb. For this purpose the invertedbulb may be provided with a protecting shield 20 as shown in Fig. 4which, in the illustrated process, covers the skirt portion of the bulband protects it up to the line of maximum bulb diameter. The shield 20may be of rubber, clay or any other suitable material. The shielded bulbin is now rotated within range of a spray nozzle 2| by which metallicliquid, such as silver or aluminum lacquer, may be delivered to theexposed bowl portion of the bulb to form an external metallic coating 22in an area coex-v tensive or substantially coextensive with the thinnerinternal coating 15. The relation of the two coatings l5 and 22 isindicated in the fragmentary view of Fig. 5 which shows a portion of alamp and its coatings on an enlarged and somewhat exaggerated scale. Itwill be noted that the external metallic coating 22 is substantiallythicker than the internal metallic coating l5 and in practice therewould be a greater difference between the thickness of these coatingsthan is indicated in Fig. 5. In any case however all pinholes or defectswhich may have occurred in the internal coating I5 are backed up andcovered by the external coating 22 so that a continuous anduninterrupted composite reflecting surface is insured in the lamp.

While a metallic external coating has been referred to specifically inthe foregoing description, I contemplate employing any suitable materialfor providing a continuous opaque or semiopaque surface such as waterglass paint including any desired pigment. Under some circumstancesthe external coating may be black in color so as better to radiate heattransmitted to it through the lamp bulb from the inner reflectingsurface.

Having thus disclosed my invention and described specific embodimentsthereof for purposes of illustration but not by way of limitation Iclaim as new and desire to secure by Letters Patent:

1. A reflecting electric lamp comprising a pearshaped bulb containing alight source and having a thin metallic reflecting coating upon itsinner surface in an area enclosing the light source and extendingapproximately to the line of maximum bulb diameter, and an externalmetallic coating upon a substantially coextensive area on its outersurface, the two coatings supplementing each other in providing aportion of the bulb with an inwardly directed and uninterruptedreflecting surface.

2. A reflecting electric lamp comprising a bulb containing a lightsource and having a thin metallic coating of high luster upon a definitearea of its inner wall, and a thicker supplementary metallic coatingupon its outer wall in a substantially coincident area and presenting aninwardly directed reflecting coating.

3. A reflecting electric lamp comprising a bulb containing a lightsource and having a thin discontinuous metallic film upon a portion ofits inner surface, and an external metallic coating substantiallycoextensive with said film and forming in combination therewith acontinuous reflecting surface.

4. A reflecting electric lamp comprising a bulb containing a lightsource and having a thin reflecting coating upon its inner surface whichis not free from pin holes, and a substantially opaque external coatingupon a coextensive area of its outer surface presenting an inwardlydirected reflecting surface outside the pin holes of said innerreflecting surface.

5. A reflecting lamp comprising a bulb containing alight source andhaving an internal reflecting coating of silver approachingmono-molecular thinness upon adefinite area of its inner CLARENCEBIRDSEYE.

